Methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most dangerous infectious agents in the U.S. and elsewhere, with a higher mortality rate than HIV-AIDS. MRSA is a strain of Staphylococcus aureus (S. aureus) bacteria, a common type of bacteria that may live on the skin and in the nasal passages of healthy people. MRSA does not respond to some of the antibiotics generally used to treat staphylococcal and other bacterial infections. MRSA is also called multidrug-resistant Staphylococcus aureus. 
Healthcare-associated MRSA (HA-MRSA) infections occur in people who are or have recently been in a hospital or other health-care facility. Many people may be at risk of MRSA infection due to receiving healthcare services in an environment where the MRSA bacteria are colonized on surfaces, healthcare workers, the patient or other patients. Community-associated MRSA (CA-MRSA) infections occur in otherwise healthy people who have not recently been in the hospital. In fact, MRSA has become a primary cause of skin and soft tissue infections among persons without extensive exposure to healthcare settings, and the outbreaks have occurred in athletic team facilities, correctional facilities, and military basic training camps.
HA-MRSA and CA-MRSA typically have differing antibiotic resistance patterns, requiring extensive susceptibility testing to identify appropriate treatment regimens for each case. In addition to methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains, there are CNS, or CoNS, (coagulase-negative staphylococci) species, close relatives of the bacterium Staphylococcus aureus, commonly found in humans. Many strains of CNS are also resistant to methicillin (MRCNS) using a similar SCCmec gene cassette mechanism as MRSA. Specifically, methicillin-resistant S. epidermidis (MRSE) is the strain in the CNS species most commonly seen among MRCNS carriers. Among immunocompromised patients, MRCNS, especially MRSE, can lead to infections and is common cause of wound, blood, and respiratory infections. MRSE can cause severe infections in immune-suppressed patients and those with central venous catheters.
Because of MRSA's resistance to multiple antibiotics, new and broad-spectrum antibiotics are often deployed against MRSA, for example, vancomycin, aminoglycoside, penicillin, macrolide, tetracycline and other antibiotics are the alternatives for MRSA treatment. However, MRSA has a potential to develop resistance to antibiotics to which it once was susceptible. Therefore, a rapid, accurate, sensitive and efficient method of determining the evolved antimicrobial resistance for Staphylococcus strains including MRSA, MSSA, MRCNS and MSCNS is greatly needed, so that an antibiotic will not be prescribed for infection treatment if the strain has already acquired resistance to the antibiotic agent that once was effective.